1. Field of the Invention
The present invention generally relates to an improved three-phase direct-current (DC) brushless motor with Hall elements, and more particularly, to a three-phase DC brushless motor in which the required voltage for the driving circuit is obtained by use of suitable arrangement of the Hall elements with the circuit.
2. Description of the Prior Art
The structure of a DC brushless motor is different from that of a typical DC motor in that the former is the inside-out design of the latter. In an xe2x80x9cinside-outxe2x80x9d design of a DC brushless motor, the rotating portion, i.e., the rotor, is on the outside of the stator. The stationary portion, i.e., stator, is formed by the inside of the machine and is inserted down the axis of the dipole field. The cylindrical rotor contains an array of identical permanent magnets that provide a uniform dipole field. The windings of the motor are placed in or on the stator. The stator windings are then xe2x80x9cswitchedxe2x80x9d or xe2x80x9ccommutatedxe2x80x9d to provide a DC motor/generator much the same as in a conventional DC motor.
The operation mode of a DC brushless motor is also different from that of a typical DC motor in that the commutation of the former can be performed by electronic means using switching circuits and the latter by mechanical means using brushes. Therefore, the undesired problems related to mechanical structure can be overcome by replacing the mechanical means with electronic means such as power semiconductor devices or ICs for signal processing so as to control the three-phase current of the DC motor and achieve better operation characteristics.
Please refer to FIG. 1, which shows a circuit diagram illustrating one embodiment of a DC brushless motor in the prior art. In the drawing, a DC brushless motor 1 is a bidirectional motor connected to a control circuit 6 through a Hall element signal line 5, wherein the control circuit 6 outputs a plurality of switching signals required for a driving circuit 7. Since the DC brushless motor 1 is a three-phase control unit, it is connected to the driving circuit 7 at a first terminal 2, a second terminal 3, and a third terminal 4. As can be seen in FIG. 1, the required control signals for the conventional embodiment of the driving circuit 7 are a set of three-phase control signals RL, RU, SL, SU, TL, and TU, which lead to magnetic flux through a magnet on the rotor inside the DC brushless motor 1 induced by three Hall elements and output an induced voltage into the control circuit 6.
FIG. 2 shows a functional block diagram illustrating one embodiment in the prior art. In the drawing, there are provided three Hall elements, namely Hall element I 21, Hall element II 22, and Hall element III 23. With the three Hall elements properly connected to a first motor driving circuit 20, the magnitude of the magnetic field 24 between the stator and the rotor and the variation of the magnetic flux during the operation of the DC brushless motor are detected so as to obtain the induced voltages VA, VB, and VC. The induced voltages VA, VB, and VC are input into the first motor driving circuit 20, which outputs the control voltage signals to the DC brushless motor.
As mentioned above, it is known that in the prior art three Hall elements are utilized to complete the operation of a DC brushless motor. However, there is a need for improved precision and manufacturing cost. In order to meet the requirement for higher precision and lower manufacturing cost, a better design for improvement has been proposed.
It is therefore the primary object of the present invention to provide an improved three-phase direct-current (DC) brushless motor with Hall elements, in which two Hall elements instead of three Hall elements are used to sense the variation of the magnetic flux during the operation of the DC brushless motor so as to reduce the manufacturing cost and also improve the efficiency of the motor.
To accomplish the foregoing object, the present invention provides an improved three-phase DC brushless motor utilizing two Hall elements placed upon the driving circuit so as to sense the variation of the magnetic flux during the operation of the DC brushless motor and output a voltage induced by the variation of the magnetic flux to the driving circuit, wherein the driving circuit controls the DC brushless motor by the induced voltage.
It is preferable that a third voltage required for the driving circuit to control the DC brushless motor is obtained by sampling and processing the voltages induced respectively by the two Hall elements.
It is preferable that the two Hall elements are placed upon the driving circuit and the arrangement of the Hall elements forms a angle with respect to the rotor inside the DC brushless motor.